DE 3 422 920 describes coatings for steel pipes, including successively a layer of epoxy resin, a layer of grafted polypropylene and finally an external layer of a mixture of polypropylene and of a polypropylene/polyethylene block copolymer. The glass transition temperature (Tg) of the epoxy resin is between 80 and 94.degree. C. These coatings are suitable for hot water at 90.degree. C.
Re 30 006 describes coatings for steel pipes, including successively an epoxy resin and a polyethylene modified by grafting or copolymerization with maleic anhydride.
Epoxy resins are not flexible enough and are not perfect for protection against moisture.
EP 185 058 describes telecommunication cables coated with polyurethanes for protection against moisture, but these cables do not have a thermoplastic coating.